This invention relates generally to the field of rotating mechanical devices, and more particularly, but not by way of limitation, to the reduction of bearing contaminant migration from a cartridge bearing assembly of a hard disc drive actuator assembly.
Modern hard disc drives comprise one or more rigid discs that are coated with a magnetizable medium and mounted on the hub of a spindle motor for rotation at a constant high speed. Information is stored on the discs in a plurality of concentric circular tracks by an array of transducers (xe2x80x9cheadsxe2x80x9d) mounted to a radial actuator for movement of the heads relative to the discs.
Typically, such radial actuators employ a voice coil motor to position the heads with respect to the disc surfaces. The heads are mounted via flexures at the ends of a plurality of arms which project radially outward from an actuator body. The actuator body pivots about a shaft mounted to the disc drive housing at a position closely adjacent the outer extreme of the discs. The pivot shaft is parallel with the axis of rotation of the spindle motor and the discs, so that the heads move in a plane parallel with the surfaces of the discs.
The actuator voice coil motor includes a coil mounted on the side of the actuator body opposite the head arms so as to be immersed in the magnetic field of a magnetic circuit comprising one or more permanent magnets and magnetically permeable pole pieces. When controlled DC current is passed through the coil, an electromagnetic field is set up which interacts with the magnetic field of the magnetic circuit to cause the coil to move in accordance with the well-known Lorentz relationship. As the coil moves, the actuator body pivots about the pivot shaft and the heads move across the disc surfaces.
Control of the position of the heads is typically achieved with a closed loop servo system such as disclosed in U.S. Pat. No. 5,262,907 entitled HARD DISC DRIVE WITH IMPROVED SERVO SYSTEM, issued to Duffy et al. (Duffy ""907), the assignee of the present invention. A typical servo system utilizes servo information (written to the discs during the disc drive manufacturing process) to detect and control the position of the heads through the generation of a position error signal (PES) which is indicative of the position of the head with respect to a selected track. The PES is generated by the servo system by comparing the relative signal strengths of burst signals generated from precisely located magnetized servo fields in the servo information on the disc surface.
During track following in which a selected head is caused to follow a selected track, a servo processor compares the value of the PES to a desired value indicative of the desired position of the head to the selected track and issues a digital correction signal to the power amplifier, which in turn provides an analog current to the actuator coil to adjust the position of the head with respect to the track. During a seek operation in which a selected head is moved from an initial track to a destination track, relatively large currents are applied to the coil to initially accelerate and then decelerate the head towards the destination track. The velocity of the head is repeatedly measured and the current applied to the coil is adjusted in accordance with the difference between the actual velocity of the head and a velocity profile.
As will be recognized, a continuing trend in the industry is to provide successive generations of disc drives with ever improved capacity and performance characteristics at an ever decreasing cost. To this end, improvements are continually being made to improve disc drive data storage and transfer rates, including increases in the rotational speeds of the discs, increases in track densities and increases in the radial velocities of the heads during seek operations. However, a problem that has been experienced with increases in the radial velocities attained by heads during seeks is the migration of contaminants (such as lubricants and particulates) from the cartridge bearing assemblies used to facilitate rotation of the actuators. As will be recognized, such contaminants can adversely affect the performance of a disc drive should such contaminants migrate to the surfaces of the discs.
The problem of bearing contaminant migration to the interior environment of a disc drive is not new, per se. Particularly, the prior art includes a variety of approaches to minimize the egress of contaminants from bearings used with the spindle motors to facilitate rotation of the discs, such as exemplified by U.S. Pat. No. 5,295,029 entitled Disk Drive Including Unitary Deck for Aligning and Supporting Axially Retractable Spindle Assembly, issued Mar. 15, 1994 to Elsing et al (Elsing ""029), assigned to the assignee of the present invention. This reference teaches the use of a labyrinth seal as part of a disc drive spindle motor configuration to minimize the migration of contaminants from the spindle motor bearings to remaining portions of the interior environment of the disc drive. Other approaches have also been taken to minimize the migration of spindle motor bearing contaminants, including the use of a ferro-fluidic seal in which a magnetic fluid is disposed between closely disposed rotating and stationary portions of a spindle motor to create a barrier to the passage of contaminants through the seal. Contamination from spindle motor bearings is of particular concern due to the high rotational speeds at which the discs are now rotated (sometimes in excess of 10,000 revolutions per minute).
Although spindle motor bearings have been generally found to be the primary source for bearing-generated contaminants, attempts have also been made by disc drive manufacturers to minimize the egress of bearing contaminants from the cartridge bearing assemblies used to facilitate radial movement of disc drive actuators. One example of interest is the prior art use of a washer-type disc that is press-fitted over a stationary shaft of the cartridge bearing assembly so as to outwardly extend to a radial point that is in close proximity to a rotating portion of the cartridge bearing assembly. However, problems have been identified with this and other approaches to minimize cartridge bearing assembly contamination.
First, contaminants have been found to typically migrate in a direction away from the center of the cartridge bearing assembly as a result of centrifugal forces exerted during rotation of the actuator assembly; thus, approaches like the washer-type disc do little to prevent the migration of contaminants between the stationary disc and the rotating portion of the cartridge bearing assembly adjacent the disc. Moreover, contaminants have been found to migrate through the typical metal-to-metal contacts such as obtained from a press-fit operation, and such migration is enhanced as performance characteristics of a disc drive are increased. Bearing seal materials that are routinely used in other applications are often unsuitable for use within the interior environment of a disc drive. Finally, prior art approaches to reducing bearing contaminant migration have been found to be excessively expensive, in terms of either labor or material costs, or both.
Accordingly, there is a continual need for improvements in bearing contaminant retention methodologies that are both operationally effective and inexpensively implemented.
The present invention provides an apparatus for minimizing the migration of contaminants from the bearings of a cartridge bearing assembly of a disc drive.
In accordance with the preferred embodiment, the cartridge bearing assembly includes a stationary shaft, a bearing assembly and a cartridge bearing sleeve. The bearing assembly is disposed between and rigidly affixed to the stationary shaft and the cartridge bearing sleeve so as to facilitate radial movement of the cartridge bearing sleeve relative to the stationary shaft.
A retention disc is rigidly affixed to a portion of the cartridge bearing sleeve adjacent the bearing assembly to form a retention chamber adjacent the bearing assembly to prevent the migration of contaminants from the bearing assembly to the interior of the disc drive.
Adhesive is used to bond the retention disc to the cartridge bearing sleeve, the adhesive providing additional sealing against the passage of contaminants between the retention disc and the cartridge bearing sleeve.
A circular flange is provided at an inner diameter of the retention disc, the flange disposed in close proximity to and substantially parallel with the stationary shaft, the flange and the shaft cooperating to form a labyrinth seal to further minimize the egress of contaminants from the retention chamber to the interior environment of the disc drive.